The auditory system of the mustache bat, Pteronotus p. parnellii, is important for the study of biofeedback and neuronal mechanisms associated with signal detection and analysis. These animals Doppler shift and amplitude compensate in order to keep the echoes from fixed targest within specific frequency and intensity ranges. In this investigation behavioral and neurophysiological studies will be carried out during pendulum "flight" while the animals are actively enaged in echolocation. Both cochlear microphonic and evoked neural potentials will be recorded in response to emitted pulses and returning echoes and under conditions of quiet and noise. At the same time the accuracy of the compensation will be assessed under normal conditions and after interruption of efferent (olivocochlear) fibers to the hair cells. These studies will test hypotheses concerning the role of efferent fibers in intensity and frequency discrimination and in the detection of signals in noise; these studies will also be used to assess existing theories on the mechanisms of biosonar systems and mechanisms controlling auditory input. The structure and population density of the efferent nerves will be studied with a variety of anatomical (TEM, SEM, LM) and histochemical techniques. Fiber pathways will be traced with the use of HRP. This project is part of a long term goal of understanding neural mechanisms associated with the peripheral auditory system and with speech, hearing and associated biofeedback mechanisms.